The present invention relates to PTT staple fibres [where PTT equals poly(trimethylene terephthalate)] and to a process for the production thereof by a two-stage spinning and stretching process.
Staple fibres made from polyethylene terephthalate and melt-spinning plants for their production are known (Fournxc3xa9, Synthetische Fasern [Synthetic Fibres], Hanser Verlag [1995] pages 460-462). Owing to the different crystallization behaviour, these processes cannot readily be applied to PTT.
Processes for the production of PTT continuous filaments have also been described. Thus, Journal of Polymer Science, Part A-1, Vol. 4, 1851-1857 (1966) mentions, inter alia, PTT fibres. The high stretching ratios specified indicate an uneconomically low spinning speed. The fibre properties listed do not meet today""s market requirements.
EP 0 547 553 A1 describes the production of monofilaments at a spinning speed of 20 m/min and a production speed of 100 m/min.
EP 0 754 790 A2 describes the production of textile filaments, inter alia from PTT, by means of heating surfaces heated to high temperatures as stretching aids. There are no specific working examples.
WO 99/11845 A1 describes fibres made from PTT with a birefringence of at least 0.030. The parameters given indicate low elongation at break values of xe2x89xa690%, which do not facilitate a stretching ratio that is sufficiently high for further conversion into staple fibres and are therefore unsuitable.
WO 99-27168 A1 discloses a high-speed spin-stretch process for the production of PTT filaments which are wound onto yam spools. High throughputs and tow baling for the production of staple fibres cannot be derived therefrom.
CA 86:122866 regarding JP 52-08124 A relates to the treatment of PTT multifilaments with heating devices, where the stretching ratio of 33% to be applied is unsuitable for the production of staple fibres.
CA 86:122865 regarding JP 52-08123 A describes the use of a high stretching ratio of 300%, which is desired per se, in the production of PTT fibres. However, the spinning speed of 360 m/min which is practised to this end is so low that the economic efficiency of the process is put in doubt.
CA 86:122856 regarding JP 52-05320 A describes the spinning of PTT, where the stretching ratio practised indicates uneconomically low spinning speeds.
The object of the present invention is to provide PTT staple fibres, where these and the textiles and home textiles, in particular carpets, produced therefrom should have a high aesthetic level and service quality compared with conventional fibres and should have environmentally friendly dyeing properties. These PTT staple fibres should be produced in a two-stage process of melt spinning and stretching which has higher economic efficiency than the above-mentioned processes for continuous filaments.
This object is achieved in accordance with the invention by PTT staple fibres and by a process for the production of PTT staple fibres having an intrinsic viscosity of at least 0.70 dl/g as described in the patent claims.
The term PTT here is taken to mean a polyester comprising at least 90 mol% of trimethylene terephthalate units. Suitable comonomers are isophthalic acid, 2,6-naphthalenedicarboxylic acid, ethylene glycol, diethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol. Preference is given to poly(trimethylene terephthalate) homopolymer, particularly preferably with a low proportion of ether groups derived from 1,3-propanediol which are formed during the production process. The intrinsic viscosity of the PTT staple fibres is in the range from 0.7 to 1.3 dl/g and particularly preferably from 0.75 to 1.15 dl/g.
The process commences from PUT melt, which is either taken directly from the polycondensation reactor in the preparation of PTT or is obtained by melting PTT granules. The polymer melt may comprise conventional additives, such as dyes, matting agents, stabilisers, antistatics, lubricants and branching agents, in total amounts of from 0 to 5.0% by weight, or the additives can be added to the melt on its way to the spinnerets. Additives which significantly affect structural parameters (for example elongation at break of the strand) are excluded.
In accordance with the invention, PTT staple fibres are produced, preferably with a titre of from 0.8 to 20 den, by a two-stage spinning and stretching process which comprises the following steps:
1. The PTT melt, having a polymer melting point Tm, is fed to the spinning system at a melt temperature TS=Tm+k (xc2x0 C.), where 7xe2x89xa6kxe2x89xa663, preferably 2 xe2x89xa6kxe2x89xa641. The transport and distribution of the melt as far as the spinning beam take place here in jacketed product lines, which are heated with liquid and/or vapour-form heat transfer medium in the outer jacket of the lines at a temperature in the range from 234 to 290xc2x0 C. Other types of heating are possible. The wall shear rates of the melt in the line system are from 2 to 128 secxe2x88x921, preferably from 3.5 to 16 secxe2x88x921, in the pipelines and from 12 to 128 secxe2x88x921 in static mixing elements installed within certain line sections. The shear rate xcex3 here is defined by the empty pipe shear rate times the mixer factor m, where the mixer factor is a characteristic parameter of the mixer type and is about 3.5-4 for Sulzer SMXL models. The shear rate xcex3 in secxe2x88x921 is calculated from       γ    ⁢          xe2x80x83        ⁢    γ    =                    4        ·                  10          3                ·        G                    π        ·        δ        ·                  R          3                ·        60              ·    m  
where G=polymer transport rate (g/min),
xcex4=nominal density of the polymer (g/cm3),
R=empty pipe radius [mm].
The mean residence time of the melt in the product line as far as entry into the spinning beam is a maximum of 30 minutes, preferably a maximum of 25 minutes. The line temperature T1 is preferably set within the above limits in such a way that it is in the range T1=TSxc2x115xc2x0 C. The product line optionally includes at least one booster pump, at least one polymer filter, at least one polymer heat exchanger and at least one shut-off and distribution valve.
2. In the spinning beam, the PTT melt is fed to at least one spinning pump, fed at a constant transport rate, set through the choice of the pump speed, to at least one spin pack by means of the pressure built up by the pump and forced through distributor devices, filter and shear media within the spin pack and spun through the holes of the spinneret plate to give melt strands. The spinneret holes may be circular or designed in any desired other geometry.
The spin pack can be inserted into the spinning beam from below and can have a cylindrical geometry, with the holes in the spinneret plate being distributed symmetrically over an annular area.
The spinneret plates have a hole density of from 0.3 to 20 holes/cm2. The spinneret hole diameter D is selected as a function of the hole throughput in accordance with                     F        ⁡                  (                      g            /            min                    )                                      ζ          ⁡                      (                          g              /                              cm                3                                      )                          ·        π        ·        2              2    ≥      D    ⁡          (      mm      )        ≥                    F        ⁡                  (                      g            /            min                    )                                      ζ          ⁡                      (                          g              /                              cm                3                                      )                          ·        π        ·        7              2  
where xcex6 is the density of the melt and, for homo-PTT, is 1.11 g/cm3.
The flow rate F per spinneret hole, based on the fibre titre, is in the range F(g/min)/titre(dtex)=(0.14 to 0.66).
The residence time of the melt in the spin pack is at most 4 minutes. The spinning draft is selected between 1:30 and 1:160 and is determined in a known manner from the ratio of the take-off rate to the injection rate at the spinneret holes.
The heating of the spinning beam is selected in the range 234-290xc2x0 C. in such a way that the following relationship applies: TB (xc2x0 C.)=TS+dTW+4/100 dp(bar)xc2x115, where dTW=change in the melt temperature in the heat exchanger, which is set positive for heating and negative for cooling and is equal to 0 in the case of plants with no heat exchanger, dp(bar)=total pressure drop of the melt as far as the exit from the spinneret plate.
3. The melt strands are cooled by means of turbulence-free cooling air at a temperature between 5 and 25xc2x0 C., preferably from 8 to 18xc2x0 C., flowing in perpendicularly to the strand running direction. The mean outflow speed of the cooling air from the rectifier is from 0.5 to 2.0 m/sec. The blow zone lengths are between 50 and 2000 mm, preferably from 150 to 600 mm, in the case of cooling-air systems which are concentric to the strand run (radial blowing) and from 500 to 2000 mm in the case of blow shafts with cross-flow blowing, and particularly preferably 150-300 mm for fibre titres xe2x89xa65 den/filamnent and from 300 to 600 mm for 12-20 den/filament.
4. The cooled strands are finished with an oil-water mixture. The amount of water on the strands is adjusted to between 12 and 30% by weight, preferably from 18 to 25%.
Immediately or shortly thereafter, the filaments from a spinning position are gathered together to form a filament bundle. The filament bundles from the individual positions are subsequently combined to form a spun tow, preferably at the spinning wall. The spun tow is taken off at speeds in the range from 600 to 2000 m/min by means of a take-off unit, and the spun tow is then deposited in a can.
5. The cans are placed together to form a creel in a creel chamber held at a temperature of from 15xc2x0 C. to 35xc2x0 C., preferably from 20xc2x0 C. to 27xc2x0 C., and fed to a fibre drawing frame. The spun tow from the cans is taken off via a feed unit, after which at least one full tow is formed from individual spun tows by means of a comb.
The full tows are stretched in at least one stretching stage, optionally with supply of a temperature-controlled oil/water mixture. A temperature in the range 20-100xc2x0 C. should be maintained here. The stretching ratio (SR) is selected in accordance with the strand elongation Rd in such a way that SR(%)=1+xcex1xc2x7Rd/100, where xcex1=0.25 to 0.75, with relatively small xcex1 values being preferred for large titres and relatively large a values being preferred for smaller titres.
This is then optionally followed, depending on the maximum temperature of 210xc2x0 C. used, by heat setting and relaxation in at least one stage. The stretching, heat setting and relaxation are carried out at speeds of from 25 to 400 m/min.
The discharge speed from the relaxation zone is preferably at least 90 m/min, particularly preferably 180 m/min, at titres xe2x89xa65 dtex.
The cooling of the full tow to below the glass transition temperature is preferably carried out using an oil/water mixture or using pure water.
6. The individual tows are subsequently laid together to form at least one tow, and each tow is fed to a stuffer box crimping machine. Post-softening using an oil/water mixture and/or steam treatment of the tow as crimping aid is optionally carried out. The subsequent drying of the tow in at least one dryer stage is carried out with residence times of from 0.5 to 10 minutes at temperatures of from 30 to 200xc2x0 C., preferably from 60 to 165xc2x0 C. The resultant tow(s) can subsequently be cut to a staple length of preferably between 6 and 200 mm. Alternatively, it is possible for the tow(s) to be packed and converted into staple fibres later in a separate operation.
In this way, PTT staple fibres are obtained which have a novel, hitherto unknown combination of properties for staple fibres which are evident as follows: high permanent elasticity and bulk of the fibres, a novel combination of high viscosity together with the mechanical parameters described by the stress-strain diagram, of modulus values and thermal shrinkage stability, with dyeing with dispersion dyes being possible without addition of carrier/dye absorption aids, and the fibres having permanently stain-repellent properties.
Characteristic features of the PTT staple fibres according to the invention are an LASE value at 10% elongation of from 5 to 12 cN/tex, a secant modulus at an elongation value=elongation at break minus 45% (but at least 5%) of less than 1.0 cN/tex per 1% change in elongation, and a crimp stability of greater than 75%. This combination of properties results in extremely desirable aesthetics and service quality compared with conventional fibres. The dyeing properties result in considerably better environmental friendliness of the post-processing process. The areas of application are to be regarded as being in textiles and home textiles, in particular carpets.